Ballast circuits are generally used in gaseous discharge lighting systems to regulate the supply of electrical power to the lamp. The type and size of lamp to be operated are typically determinative of how the ballast circuit will be configured. For example, high intensity discharge (HID) lamps such as mercury, metal halide, and high pressure sodium lamps are usually operated at high wattage and require a different ballast circuit than lamps such as fluorescent lamps which operate at relatively low wattage. Even among lamps of the same type (i.e., mercury, metal halide, high pressure sodium, fluorescent, etc.) the specific lamp wattage can vary, which in turn requires a corresponding variance of elements within the ballast circuit in order to optimize operation of the lamps. As a result, conventional ballast circuits are unable to accommodate proper operation of different lamps types and/or lamps of the same type which operate at different wattages.
Typical ballast circuits include a starting circuit for igniting the lamp and an operating LCR (Inductor-Capacitor-Resistor) circuit for sustaining lamp ignition. In a typical ballast circuit, the same inductor is used to produce the electrical excitation necessary to ignite as well as to operate the lamp. In order to withstand large operating currents for prolonged periods of time, the inductor must be physically large, which increases the size, cost, and weight of the ballast circuit. These large inductors often operate at or near 100 percent of their duty cycle, which in turn results in significant power consumption and heating. Reliability also suffers as the effects of heating increase the failure rate of circuit components. In addition, the versatility of the lamp operating circuit suffers since the inductor used in the operating circuit must be within the operating parameters of the particular lamp being operated. Different lamps which operate at different wattages typically require a different or unique inductor to allow for proper operation of the lamp at the correct frequency. Consequently, ballast circuit designers often struggle in their attempt to find the optimal inductor for a particular lighting application.
What is needed, therefore, is a ballast circuit that eliminates one or more disadvantages of prior art ballast circuits.